Photochromic copying method

ABSTRACT

A stable image can be obtained by the copying method which comprises: applying image-wise ultraviolet rays having a wavelength lambda 1 corresponding to the absorption wavelength range of a spiropyran compound to a photochromic copying material comprising a support and a photosensitive layer containing the spiropyran compound, an aromatic or a cyclic ketone and a doped semi-conductive metal oxide; and subsequently applying ultraviolet rays having a wavelength lambda 2 capable of decomposing said ketone - either in the presence of an alcohol in the case of the ketone being aromatic or in the absence of alcohol in the case of the ketone being cyclic - to the whole surface of said copying material, or vice versa.

I United States Patent 1 1 [111 3,871,886

Robillard 5] Mar. 18, 1975 [54] PHOTOCHROMIC COPYING METHOD 3,486,899 12/1969 Brown 96/90 PC 3,660,086 5/1972 Tamai 96/90 PC [75] Inventor: zg' g Achllle Vmy, 3,704,127 11/1972 Dessauer 96/48 R 73 Assignee: Kabushiki Kaisha Ricoh, Tokyo, Primary Examiner-Mary Kelley 13 an Attorney, Agent, or Firm-Cooper, Dunham, Clark,

p G ff & M 221 Filed: June 21, 1973 [2]] App]. No.: 372,405 [57] ABSTRACT A stable image can be obtained by the copying 30 Foreign Application p i Data method which comprises: applymg 1mage-wise ultravi- June 27 197.) France 72 23184 olet rays havmga wavelength A, corresponding to the Jul France 721M945 absorption wavelength range of a spiropyrancomy pound to a photochromic copying material comprising 21 us. c1. 96/48 R, 96/90 R, 96/90 PC a .Support and a phomsensitive layer comalning 1] [M G036 5/24 G03: H52 sp1ropyran compound, an aromat1c or a cyclic ketone 81 i 96/90 PC R 48 R and a doped semi-conductive metal oxide; and subsequently applying ultraviolet rays having a wavelength [s6] References Cited A capable of decomposing said ketone either in the presence of an alcohol in the case of the ketone being UNITED STATES PATENTS aromatic or in the absence of alcohol in the case of 3.3l7,32l 5/l967 Chopoorian 350/l60 P the ketone be'mg cyclic to the whok; urface of aid 2:22:12 @4822 22122 :2 or I 3,485,765 l2/1969 Newland 96/90 PC 7 Claims, N0 Drawings PHOTOCHROMIC COPYING METHOD BACKGROUND OF THE INVENTION a. Field of the Invention The present invention relates to a copying method capable of forming a stable image as well as to photochromic copying materials useful in such method.

b. Description of the Prior Art In the method utilizing photochromism, that is, the method utilizing a photochemically obtained reaction product for recording or copying purpose, the process of converting achromatic compounds into a chromatic compounds, or vice versa, is already known. Such utilization of photochromism of photochromatic compounds makes it possible to raise the resolving power to the molecular level rather than the particle level, so that it is possible to form high quality images. However, photochromism is a reversible reaction. The process therefore is defective since the image tends to fade with the lapse of time. This problem has been a serious obstacle to utilization of photochromic compounds for photography and copying purpose.

There is, therefore, a need for a method of fixing the image formed by photochromic reaction so that it does not fade.

SUMMARY OF THE INVENTION The present invention provides novel methods of reproduction to produce stable, lasting images, wherein a photochromic copying material containing at least one spiropyran of indoline or benzothiazoline as the photochromic compound is employed, and the image area (which assumes a chromic form) and the nonimage area (which assumes an achromic form) are respectively made to be irreversible, that is they are fixed. More specifically, the present invention provides methods of reproduction which include the steps of applying image-wise ultraviolet rays having the wavelength A 1 corresponding to the absorption wavelength range of a spiropyran compound to a photochromic copying material comprising a support coated with a photosensitive layer containing the spiropyran compound, an aromatic or a cyclic ketone and a doped semi conductive metal oxide; and subsequently applying ultraviolet rays having the wavelength A 2 capable of decomposing said ketone either in the presence of an alcohol in the case of aromatic ketones or in the absence of alcohol in the case of the cyclic ketones to the whole surface of said copying material.

In the present invention these steps may be reversible.

It is well known that a spiropyran of indoline or benzothiazoline is converted to a chromatic merocyanine as a result of opening of the pyran ring under the influence of light and that the reaction is reversible. This process may be expressed by the following formula.

spiropyran (achromatic form) merocyanine (chromatic form) Spiropyrans of indolines or benzothiaiolines which are useful in the present invention includes those represented by the following general formulas:

wherein:

R and R -represent alkyl groups having l-3 carbon atoms respectively; R represents alkyl groups having l-3 carbon atoms or phenyl; R represents H, alkyl groups having l-3 carbon atoms, alkoxy groups having l-3 carbon atoms or halogen atoms; R represents H, halogen atoms or nitro group; R represents alkyl groups having l-6 carbon atoms, benzyl group or phenyl methyl group; R represents alkyl groups having l-3 carbon atoms, naphthyl group, phenyl group, cyclohexyl group, methoxyphenyl group, hydroxyphenyl group, halogen-substituted phenyl groups or a thiophenyl group; R represents H, OH or SCH and R representss OH or alkoxy groups having l -3 carbon atoms.

Compounds illustrative of spiropyrans useful in this invention include, for example,

1. a-compound of the general formula (I) wherein R R2 CH3, R3 C6H5, R4 OCHg, and R5 2. a compound of the general formula (I) wherein R R R CH and R R Br;

3. a compound of the general formula (I) wherein R R R CH R H, and R N0 4. acompound of general formula (II) wherein R R CH R H, and R OCH 5. a compound of general formula (II) wherein R CH3, I

R H, and R OCH;,; 10. a compound of general formula (II) wherein R CH3 r R8 H, and R9 l l. a compound of general formula (II) wherein R R7 @-ocu R H, and R OCH 12. a compound of general formula (II) wherein R OCH,,

R H, and R OCH 13. a compound of general formula (ll) wherein R R CH and R R OH;

14. a compound of general formula (II), wherein R R CH R SCH and R OH or OCH 15. a compound of general formula (ll) wherein R isopropyl, n-hexyl, benzyl or phenylethyl group, R CH R OH, and R OCH;,;

16. a compound of general formula (II), wherein R CH R naphthyl, cyclohexyl, S-phenyl, phenyl, chloro-4-phenyl, bromo-4-phenyl, methoxy-4-phenyl or hydroxy-4-phenyl or hydroxy-4-phenyl group, R OH, and R OCH;,; etc.

The molecule of a spiropyran (closed ring form) has a molecular structure in which two surfaces meeting at right angles with each other have conjugated portions, which are linked by saturated carbon atoms. When this molecule is adsorbed on the surface of an adsorbent, the bond with the adsorbent is effected through a single or several benzene rings within the molecule. As a result of photochromism, at the time when the pyran ring opens at the C bond, the second section of the molecule of the spiropyran becomes freely rotatable centering around carbon atoms linking both planes. This section then becomes parallel to the surface of the adsorbent. As a result it bonds to the adsorbent. This bond resists reclosing of the ring so that the chromatic .form of spiropyran (i.e., merocyanine) is fixed. When one or several of the substituents R -R or R -R is aromatic, the strength of the molecular bond to the adsorbent is augmented and the stability of the openedring form is increased.

Any of a variety of semi-conductive adsorbents may be utilized for the purpose of stabilizing the chromatic merocyanine. Doped metal oxides are especially useful. The following materials are illustrative of metal oxides as well as the doping agent applicable thereto which may be employed in the present invention.

metal oxide doping agent metal oxide doping agent TiO ITiO Cu Zr 0 La/Cu TiO, Ce/Ni ZnO Cu TiO La/Ni ZnO Ce/Ni TiO Ce/Cu ZnO Ni ZrO, Ce/Ni ZnO Al/Ni The doped metal oxides for use in the present invention can be prepared, for instance, by the following procedure.

The metal oxide powder is dipped in a solution of a doping metallic salt, whereby doping is effected. Subsequent to this operation the material is heat treated to diffuse the metal ions adsorbed onto the surface of the particle of said substance into the core of the particle. The thus processed powder is next subjected to mechanical stirring for about one-half hour in a large volume of solution, filtered, and then introduced into a furnace as a thin layer of powder and heated at a temperature of 300-500C for several hours.

In this connection, the temperature of the furnace and the time of treatment vary with the properties of the pigment as well as the rate of diffusion of the metal ions adsorbed to the surface of the pigment particle toward the core thereof.

To be more precise, the amount of a metal adsorbed to the surface of a particle having a grain size of 10 1.1. within a l percent solution is to the extent of 10* 10 metal atoms per crystal latticeatom of the pigment. Next, the powder is separated from the solution by filtration and is washed several times with a small quantity of distilled water. Next, the powder is filtered again, and then is placed in the boat of furnace in the form of a thin layer for further thermal diffusion. This diffusion is performed twicefirst, at the temperature of T for the period of :1 hours, and next at the temperature of T for the period of hours. Upon finishing the above operation, the temperature of the furnace is slowly restored to room temperature. Next, the resulting aggregated powder in the form of solid lumps is crushed, and then re-crushed into small spheroids by several hours treatment in a grinder so that the resulting particles may pass a 44 11, mesh sieve.

Table 1 below shows a variety of solutions applicable to various pigments, the temperature for heat treatment and the time thereof.

Table ll shows the properties of the starting oxides.

Table l Pigment Crystal form Solution of Concentration T t T t doping agent '7: "C hr. C hr Ti(). ,Rl.l6 rutilc Cu 50, 1 I00 I 420 4 'l'i(). RL futile Cc(SO. NiCl 0.92-0.78 I00 I 400 4 'li() RL rutile Cc(SO ),Ni(l 0.92-0.78 200 l 380 4 TiO AT 1 miutase LaCl, NlCl l -0.78 200 l 350 6 v TiO AT 4 anatusc Cu(SO.,) CuSO,. ().92- l 200 l 320 6 2110 Ncigc Zincitc CUSO; l I00 I 475 5 ZnO Kadox l5 Zincitc Cc(SO NiCl 0.92-0.78 l 450 5 ZnO Kzltlox 72 Zincitc NiCl-g 0.78 I00 I 450 5 ZnO Photox 801 Zincitc Lacl NiCl l -0.78 100 l 450 5 ZrO Baddclcyitc Cc(SO NiCl 0.92-0.78 200 l 500 4 Zr0 Baddcleyitc LaCl CuSO, 1 '-0.78 200 l 500 4 Table ll Pigment Kind Density Purity Impurities Grain size pH Origin Anatasc AT 1 3.8 98.0 A], Si 0.03 6.8 TM Anatase AT 4 3.7 96.0 Al, Si 0.3 6.8 TM Rutile RL 16 4.0 90.0 Al. Si 0.35 6.8 TM

78 Rutilc RL 75 3.8 86.0 Al, Si 0.35 38 TM .0

Table I1 Continued Pigment Kind Density Purity Impurities Grain size pH Origin Rutilc RL 90 4.0 96.0 Zn, Al, Si 0.40 8.0 TM Zinc oxide Ncigc C 5.67 99.7 Pb, Cd, S 0.27 7.0 VM Zinc oxide USP 12 5.60 99.8 PbO, A5 0 0.30 7.0 NJZ Zinc oxide Photox 801 5.65 99.8 PbO, CdO 0.37 7.0

(A) TM: Fahriqucs dc Produils chimiques de Thann cl Mulhouse VM: Sociclc dc Ia Vicillc Montaigne NJZ: New Jersey Zinc Company The above spiropyrans and doped metal oxides have been cited only for the purpose of illustration, and it will be understood that the spiropyrans and doped metal oxide applicable to the present invention are not limited by these illustrations, but that a wide variety of other analagous materials may be used. One skilled in the art will have no difficulty in selecting other pairs of adsorbents and spiropyrans, once having the benefit of this disclosure. With this in view, it is advisable to refer to the following literature articles:

The method of fixing the non-image area will now be discussed. v For the purpose of color development of a spiropyran of indolines or benzothiazolines per se, a large quantity of optical energy is required, so that for practical purposes it is advisable to use a sensitizer. According to the present invention, specific sensitizers are employed, and at the time of fixing the non-image area, said sensitizer is converted into a compound which does not have a substantial sensitizing effect, whereby fixation is performed.

sensitizers useful in the present invention include keton'es such as those already known as sensitizers for use in photochromism of spiropyran.

When an aromatic ketone is employed as the sensitizer, this ketone is converted into a compound not having a sensitizing effect by application of light in the presence of an alcohol. When a cylic ketone such as a lactone is used as a sensitizer its sensitizing activity can be destroyed by mere application of light having a specific wavelength without using an alcohol. The following equations illustrate examples of photochemical decomposition of aromatic and cyclic ketonesin accordance with this invention.

a. Photochemical reduction of aromatic ketone with alcohol:

benzophenone isopropyl OH OH '011- -cu alcohol 3 j 3 if CH3 '1' (CH3) CHOH O Bipheny1-6-acetophenone t ri ketoindane 6. Photochemical decomposition of cyclic ketone:

o CH3CHO a e o 0 11,,

A -propio1actone Photochromic copying materials according to the present invention may be prepared by applying a photosensitive liquid comprising a spiropyran compound, a semi-conductor doped with a metal, and a sensitizer selected from the group of aromatic ketones and cyclic ketones onto a support by coating or impregnation. On this occasion, it is of course possible to bind the photosensitive layer to the support (such as paper, synthetic resin film, etc.) by adding any known resinous binder to said photosensitive liquid. Suitable binders include for example, acrylic, methacrylic, alkyl, silicone and styrene resins. When the layer is coated on the support the thickness of the layer is normally from about 1 to 50 microns.

Typically, the amount of the sensitizer for use in the present invention is from about lO' *-O.5 parts by weight thereof per 1 part by weight of the spiropyran compound employed. The amount of doped semiconductor will be at least sufficient to adsorb the selected spiropyran compound.

To explain the method of forming an image under the present invention, rays of light having the wavelength A, corresponding to the absorption wavelength range of spiropyran are first applied image-wise onto a photochromic material prepared as above. Through this process, the portion of said photochromic material exposed to light becomes irreversively colored. Next, fixation of the non-image area is performed through the process comprising coating an alcohol such as isopropyl alcohol on the whole surface of the photochromic material and applying rays of light having the wavelength capable of decomposing the aromatic ketone to said material coated with alcohol in the case of employing an aromatic ketone as the sensitizer, or through the process of just applying rays of light having the wavelength A capable of decomposing the cyclic ketone to the photochromic material intact in the case of employing a cyclic ketone as the sensitizer. The absorption wavelength A, of spiropyran varies with the kind thereof, and it is in the range of about 2800-4500A.

The wavelength A for use in decomposing ketones also varies with the kind thereof, and it is in the range of 2800-6000A. Accordingly, in the ease of employing a cyclic ketone as the sensitizer, it is necessary to employ a spiropyran having an absorption wavelength A, falling within the range of wavelengths not decomposing said cyclic ketone. The above operations may be reversed.

(see example 4). The selective sensitization operated in the process of the invention permits the obtaining of an increase of the sensitivity of the photochromic composition, that is to say an increase in the quantum yield of this composition. If M is the concentration of spiropyran, 1 is the quantum yield of the photochromic reaction, r, is the time of exposure to wavelength M, m is the concentration of sensitizer, 1 is the quantum yield of the photochromic reaction of destruction of the sen sitizer and t the time of exposure to A one obtains the expression 51 A (coefficient of 2 2 Amplification) m as in general 2 one has A 5 in the case of examples 1 to 4 one obtains, therefore, coefficients of the order of 40, 4, 770 and 3, respectively.

The following non-limiting examples are given by way of illustration only.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 A composition according to the present invention was prepared by thoroughly mixing the following components.

of benzophenone By coating this photosensitive liquid onto a polyester film, a photochromic copying material was obtained.

Example 2 A composition according to the present invention was prepared by thoroughly mixing the following components.

TiO doped with La/Ni IOOg Pliolite S-7 53g toluene l00ml spiropyran in Example I lOml biphenyl-4-acetophenonc (0.45 wtfk isopropyl alcohol solution By coating this composition onto a polyester film, photochromic copying material was obtained.

Example 3 A composition according to the present invention 5 was prepared by thoroughly mixing the following components.

TiO doped with Ce/Cu 100g Pliolite S-7 53g toluene 100ml 2 wt.7r toluene solution of spiropyran expressed by general formula (I) isopropyl alcohol solution) lOml By coating this composition onto a polyester film, a photochromic copying material was obtained.

Example 4 A composition according to the present invention was prepared by thoroughly mixing the following components.

Tio doped with Ce/Ni lOOg Pliolite S-7 53g toluene [00ml 2 wt.% isopropyl alcohol solution of spiropyran expressed by general formula (I) wherein alcohol solution) 10ml By coating this composition onto a polyester film, a photochromic copying material was obtained.

When light rays having a wavelength of 2800-4500A were applied to each of the photochromic copying materials obtained in Examples l-4 through a negative original image, there was obtained a positive image of superb quality respectively. The photographic sensitivity displayed was 100 A.S.A. or thereabouts.

Next, upon coating isopropyl alcohol onto each photochromic copying material in the state of a thin liquid, followed by applying light rays of tungsten lamp to said material, fixation of the non-image area was effected.

Further, when each of the photochromic copying materials obtained in Examples l-4 was subjected to the process comprising sufficiently applying the vapor of isopropyl alcohol, applying light rays of a tungsten lamp thereafter through a positive original image, leaving the material standing for a period of time enough for evaporation of isopropyl alcohol contained in its photosensitive layer and then applying light having a wavelength of 2800-4500A, there was obtained a positive colored image of high quality.

What is claimed is:

l. A copying method selected from the group consisting of:

A. a first method which comprises imagewise exposure of a photochromic copying material to light says having a wavelength A said copying material comprising a support and a photosensitive layer comprising (a) a spiropyran, (b) an aromatic or a cyclic ketone and (c) a semiconductive metal oxidevdoped with at least one metal;

said wavelength A, corresponding to the absorption wavelength of the spiropyran compound; said spiropyran compound having the general formula:

N O R I i 5 wherein:

R and R are alkyl containing 1 to 3 carbon atoms, R is alkyl containing 1 to 3 carbon atoms or phenyl,

R is hydrogen, alkyl containing 1 to 3 carbon atoms, alkoxy containing 1 to 3 carbon atoms or halogen,

R is hydrogen, halogen or nitro,

R is alkyl containing 1 to .6 carbon atoms, or

benzyl, 7

R is alkyl containing 1 to 3 carbon atoms, naphthyl, phenyl, cyclohexyl, methoxyphenyl, hydroxyphenyl, halogen substituted phenyl or thiophenyl,

R is hydrogen, hydroxyl, or thiomethyl, and

R is hydroxyl or alkoxy containing 1 to 3 carbon atoms;

said-ketone being selected from the group consisting of benzophenone, biphenyl-o-acetophenone, triketoindane, xanthotoxine and B-propiolactone;

said doped metal oxide being selected from the group consisting of TiO /TiO doped with Cu;

TiO doped with Ce/Ni, La/Ni or Ce/Cu', ZrO

doped with Ce/Ni, ZrO doped with La/Cu; and

ZnO doped with Cu, Ce/Ni, Ni and La/Ni; and

thereafter decomposing said ketone by exposure to light rays of wavelength A in the presence of an alcohol when said ketone is aromatic: and B. a second method which is the reverse of said first method whereby the first exposure is to light of wavelength A and the second exposure is to light of wavelength A,. 2. A method according to claim 1, wherein said spiropyran compound is selected from the group consisting of a compound of formula (I) wherein R,=R =CH R =C H R =OCH and R =,=NO

a compound of formula (I) wherein R =R =R =CH and R =R =,=Br;

a compound of formula (I) wherein R =R =R =CH R =H, and R =NO a compound of formula (II) wherein R =R =CH R,,=H, and R =OCH a compound of formula (ll) wherein R =CH a compound of formula (ll) wherein R =CH R CH R =H, and R =OCH a compound of formula (ll) wherein R =CH R SC H R =H, and R =OCH a compound of formula ([1) wherein R =CH R =C H R,,=H, and R =OCH a compound of formula (II) wherein R =CH R =H, and R,,=CH a compound of formula (ll) wherein R =CH R,,=H, and R,,==OCH a compound of formula (II) whcrcin R =CH;,,

R,,=H, and R,,=OCH a compound of formula (II) wherein R =OCh Rg H, and

a compound of formula (II) wherein R =R =CH and R,,=R =OH;

a compound of formula (ll) wherein R =R =CH R S-CH and R =OH or OCH a compound of formula (II) wherein R -isopropyl, n=hexyl, benzyl or phenylethyl group, R ==CH R,,=OH, and R =OCH and a compound of formula (ll) wherein R =CH R =naphthyl, cyclohexyl, S-phenyl, phenyl, chloro- 4-phenyl, bromo-4-phenyl, methoxy-4-phenyl or hydroxy-4-phenyl or hydroxy-4-phenyl group, R OH, and R =OCH and said alcohol is isopropyl alcohol.

3. A method according to claim 2, wherein the amount of ketone is from about l* -0.5 parts by weight per 1 part by weight of said spiropyran.

4. A method according to claim 2, wherein the alcohol is applied by coating the same onto the copying material.

5. A photochromic copying material comprising a support and a photosensitive layer comprising (a) a spiropyran, (b) an aromatic or a cyclic ketone and (c) a semiconductive metal oxide doped with at least one metal;

said wavelength A, corresponding to the absorption wavelength of the spiropyran compound; said spiropyran compound having the general formula:

C N/ o R 15 l 5 H OR R II wherein: 5 R and R are alkyl containing 1 to 3 carbon atoms,

R, is alkyl containing 1 to 3 carbon atoms or phenyl, R is hydrogen, alkyl containing l to 3 carbon atoms, alkoxy containing 1 to 3 carbon atoms or halogen,

R is hydrogen, halogen, or nitro, R is alkyl containing l to 6 carbon atoms, or benzyl, R is alkyl containing 1 to 3 carbon atoms, naphthyl, phenyl, cyclohexyl, methoxyphenyl, hydroxyphenyl, halogen substituted phenyl or thiophenyl, R is hydrogen, hydroxyl, or thiomethyl, and 0 R is hydroxyl or alkoxy containing 1 to 3 carbon 5 atoms; said ketone being selected from the group consisting of benzophenone, biphenyl-S-acetophenone, triketoindane, xanthotoxine and B-propiolactone; said doped metal oxide being selected from the group consisting of TiO /TiO doped with Cu; Ti0 doped with Ce/Ni, La/Ni or Ce/Cu; ZrO doped with Ce/Ni, ZrO doped with La/Cu; and ZnO doped with Cu, Ce/Ni, Ni and La/Ni. 6. A copying material according to claim 5, wherein said spiropyran compound is selected from the group consisting of a compound of formula (I) wherein R,=R =CH R3=C3H5, R4=OCH3, and R5=NO2; a compound of formula (I) wherein R,=R =R =CH and R =R =Br; a compound of formula (l) wherein R,=R =R CH R,,=H, and R =NO a compound of formula (ll) wherein R =R =CH R =H, and R =OCH a compound of formula (ll) wherein R C l-l a compound of formula (II) wherein R =CH R =CH R =H, and R =OCH a compound of formula (II) wherein R =CH R SC H R =H, and R =OCH a compound of formula (II) wherein R =CH R =C H R =H, and R #)CH a compound of formula (ll) wherein R =CH R,,=H, and R %CH a compound of formula (II) wherein R =CH R =H, and R =OCH a compound of formula (ll) wherein R =CH R =H, and R =OCH a compound of formula (II) wherein R =OCH OH, 7 H 

1. A COPYING METHOD SELECTED FROM THE GROUP CONSISTING OF: A. A FIRST METHOD WHICH COMPRISES IMAGEWISE EXPOSURE OF A PHOTOCHROMIC COPYING MATERIAL TO LIGHT RAYS HAVING A WAVELENGTH $1, SAID COPYING MATERIAL COMPRISING A SUPPORT AND A PHOTOSENSITIVE LAYER COMPRISING (A) A SPIROPYRAN, (B) AN AROMATIC OR A CYCLIC KETONE AND (C) A SEMICONDUCTIVE METAL OXIDE DOPED WITH AT LEAST ONE METAL, SAID WAVELENGTH $1, CORRESPONDING TO THE ABSORPTION WAVELENGTH OF THE SPIROPYRAN COMPOUND, SAID SPIROPYRAN COMPOUND HAVING THE GENERAL FORMULA:
 2. A method according to claim 1, wherein said spiropyran compound is selected from the group consisting of a compound of formula (I) wherein R1 R2 CH3, R3 C6H5, R4 OCH3, and R5 NO2; a compound of formula (I) wherein R1 R2 R3 CH3, and R4 R5 Br; a compound of formula (I) wherein R1 R2 R3 CH3, R4 H, and R5 NO2; a compound of formula (II) wherein R6 R7 CH3, R8 H, and R9 OCH3; a compound of formula (II) wherein R6 CH3,
 3. A method according to claim 2, wherein the amount of ketone is from about 10 3*0.5 parts by weight per 1 part by weight of said spiropyran.
 4. A method according to claim 2, wherein the alcohol is applied by coating the same onto the copying material.
 5. A photochromic copying material comprising a support and a photosensitive layer comprising (a) a spiropyran, (b) an aromatic or a cyclic ketone and (c) a semiconductive metal oxide doped with at least one metal; said wavelength lambda 1 corresponding to the absorption wavelength of the spiropyran compound; said spiropyran compound having the general formula:
 6. A copying material according to claim 5, wherein said spiropyran compound is selected from the group consisting of a compound of formula (I) wherein R1 R2 CH3, R3 C6H5, R4 OCH3, and R5 NO2; a compound of formula (I) wherein R1 R2 R3 CH3, and R4 R5 Br; a compound of formula (I) wherein R1 R2 R3 CH3, R4 H, and R5 NO2; a compound of formula (II) wherein R6 R7 CH3, R8 H, and R9 OCH3; a compound of formula (II) wherein R6 CH3,
 7. A copying material according to claim 5, wherein the amount of ketone employed is from about 10 3 *0.5 parts by weight per 1 part by weight of said spiropyran. 